Today, a datacenter may process different types of flows, including elephant flows and mouse flows. An elephant flow represents a long-lived flow or a continuous traffic flow that is typically associated with high volume connection. Different from an elephant flow, a mouse flow represents a short-lived flow. Mice are often associated with bursty, latency-sensitive applications, whereas elephants tend to be associated with large data transfers in which throughput is far more important than latency.
A problem with elephant flows is that they tend to fill network buffers end-to-end, and this introduces non-trivial queuing delay to anything that shares these buffers. For instance, a forwarding element may be responsible for managing several queues to forward packets, and several packets belonging to a mouse flow may be stuck in the same queue behind a group of other packets belonging to an elephant flow. In a network of elephants and mice, this means that the more latency-sensitive mice are being affected. Another problem is that mice are generally very bursty, so adaptive routing techniques are not effective with them.